The present invention relates to a method and a device for inductive transmission of electric power to a plurality of mobile consumers, as generically known from International Patent Disclosure WO-A1 96/20526.
In International Patent Disclosure WO-A1 96/20526 (corresponding to German Patent Disclosure DE 44 46 779), a method for inductive transmission of electric power from a medium-frequency source at a frequency fM to one or more mobile consumers via an extended transmission line and via inductive pickups IAXIAY, assigned to the mobile consumers, with downstream converter-actuators for adjusting the power PLX, PLY that is picked up from the transmission line and delivered to buffer stores to which the mobile consumers are connected, is disclosed, in which the transmission line is supplied from a current source with a medium-frequency current (IL) that is constant in its effective value during the power transmission.
A method and a device for inductive transmission of electric power to a plurality of mobile consumers are known from International Patent Disclosure WO 92/17929 A1 and the publication by A. W. Green and T. Boys, Power Electronics and Variable-Speed Drives, Oct. 26-28, 1994, Conference Publication No. 399, CIEE, 1994, pages 694-698, which describes the invention claimed in WO 92/17929.
As described in conjunction with FIGS. 1-3 of this publication, the current drawn from a rotary current network is rectified and delivered to an inverter, comprising. the IGBTs S3 and S4 and the magnetically coupled inductive resistors L2a and L2b, via a current actuator that comprises the IGBTs S1, S2, the diodes D1, D2, and a storage choke Ld. This inverter generates a medium-frequency alternating voltage of 10 kHz and feeds it into a parallel oscillator circuit formed by an inductive resistor L1 and a capacitor C1. The inductive resistor L1 is the transmission line, embodied as an extended double line, of a system for inductive transmission of electric power to a plurality of mobile consumers. The mobile consumers are magnetically coupled to the transmission line via inductive pickups, as shown in FIG. 8 of the publication. In turn, together with a capacitor, the coil of the inductive pickup forms a parallel oscillator circuit, as shown in FIGS. 1, 2 and 10 of the publication.
The current transmitted from the transmission line to the parallel oscillator circuit of the mobile pickup is rectified, according to FIG. 10, in a converter-actuator designated here as a pickup- controller, is then smoothed with a choke, and then, depending on the power demanded by the consumers connected to the o controller, is either delivered to the capacitor that buffer-stores the output voltage V0 of the controller, or is carried past this buffer capacitor. The decision here is made by the Schmitt trigger of the controller, which compares the output voltage V0 with a corresponding reference voltage and blocks the IGBT if the output voltage is too low, so that the current recharges the output buffer capacitor, or puts the IGBT in the conductive state, so that the current flows past the output buffer capacitor, if the output voltage V0 has exceeded an upper limit value.
In this power transmission method, as described in column 1, page 697 and in conjunction with FIG. 7 of the publication, if there are sudden load changes, then undesired transient phenomena occur in the overall transmission system, which is associated with mutual influence in terms of the energy transmission of a plurality of vehicles and necessitates additional damping provisions.
The causes of these undesired transient phenomena are as follows:
With the switching of the pickup-controller, which does not enable any infinitely variable change in the power picked up by the inductive pickup or in the voltage supplied to the transmission line, a strong excitation of the parallel oscillator circuit formed by the transmission line and the capacitor C1 in FIG. 3 becomes effective.
The energy picked up from the transmission line is first drawn from the parallel oscillator circuit; because of the inductive resistors in the supplying converter, it is only after a delay, and after a voltage change has been detected at the capacitor C1, that this energy is replenished via the supplying converter.
The object of the present invention is to provide a method for inductive transmission of electric power to a plurality of mobile consumers that has no transient phenomena in the transmission line current that is common to all the mobile consumers.
This object is attained by a maximum adjusting time which lasts for only a few half-periods of the medium frequency, the output voltage of the medium-frequency source adjusts infinitely variably to the value that corresponds to the total variable power picked up from the transmission line, and that the converter-actuator connected between the buffer memory and the inductive power pickup of each mobile consumer adjusts the mean consumer power picked up from the transmission line and delivered to the buffer memory, infinitely variably and with a limited rate of change, within an adjusting time which is longer than the adjusting time of the medium-frequency source, with the medium-frequency source having a maximum adjusting time of its output signal that is less than the adjusting time of the power pickup at the consumer can be learned from the dependent claims and the specification.
The essence of the present invention is considered to be the creation of a method and a device for inductive transmission of electric power from a stationary transmission line to mobile consumers, in which:
the transmission line is supplied with a constant medium frequency current IL from a medium-frequency source whose output voltage UL adjusts infinitely variably within a brief adjusting time TS, which lasts only a few half-periods of the medium frequency, to the variable value corresponding to the consumer power, and the rate of change of the power consumption from the transmission line via the inductive pickups of the mobile systems is limited by converter-actuators, whose adjusting time TA is longer than the adjusting time TS of the medium-frequency source, in such a way that the medium-frequency source can easily follow with the appropriate power output.
The present invention has the advantage that transient phenomena are reliably avoided. Another advantage is that at the same time, mutual influence of mobile consumers on each other can be precluded.
Compared with the prior art, the method of the present invention has the following further advantages as well:
The transmission frequency is power-independent and constant; the inductive pickups are always operated at their resonant point, that is, their operating point of optimal utilization.
Turning partial capacitors on or off in the event of load changes, as shown for instance on page 698 and described in conjunction with FIG. 12 of the publication cited as prior art, is not necessary.